This invention relates to radar systems, and more particularly, to a method of pulse compression processing which allows for detection of targets at ranges both shorter and longer than a "minimum" detection range of the radar.
In coherent array radar systems, a complex coded pulse is modulated onto a carrier and the resultant waveform is upconverted to a frequency transmitted by the radar. The received, return signal is downconverted to a frequency which is compensated for possible doppler modulation As part of processing the return signal, it is supplied to a phase detector. In general, the phase angle varies for each received pulse. Further, prior signal processors utilized a pulse compression technique which is the equivalent of a tapped delay line. A received signal, starting at the end of a transmission period, is input to the delay line and will arrive at the nth tap of the delay at a time which is a function of the propagation rate of the signal through the line. The signal has peaks representing targets reflecting the transmitted signal
It will be appreciated that during pulse transmission, the radar receiver is blanked out. As a result, if the round trip time for a transmitted signal reflected back to the radar is less than the blanking time, the peaks will occur in "blind zones", i.e. they are masked by the transmitted pulse since they are propagating through the delay line at the same time blanking is occurring. As a consequence, targets within the blind zone will not be identified during signal processing.